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Caseless ammunition
Caseless ammunition is a type of small arms ammunition that elimitates the cartridge case that typically holds the primer, propellant, and projectile together as a unit. Caseless ammunition is an attempt to reduce the weight and cost of ammunition by dispensing with the case, which is typically precision made of brass or steel, as well as simplify the operation of repeating firearms by eliminating the need to extract and eject the empty case after firing. __FORCETOC__ History Caseless ammunition, in the broad sense, is not a new concept. A number of early paper cartridge designs used a combustible "case" which left no significant residue in the action after firing; one of the earliest breech-loading rifles, the Dreyse needle-gun, used such a cartridge. It contained the powder, primer, and saboted bullet in a paper cartridge. This design was an evolution of earlier paper cartridges for externally primed muzzle loading firearms, and predated the wide adoptiong of the metallic cartridge case. The first use of caseless ammunition for use in a repeating firearm was the Rocket Ball projectile patented by Walter Hunt in 1848. A charge of black powder was placed inside a hollow at the back of a specially shaped Minie Ball. These rounds were used by Hunt in a prototype repeating lever action rifle. The later Volcanic cartridge by Smith & Wesson added a primer to the Rocket Ball, and improved on the lever action design. Similar ammunition was used by the Volcanic Repeating Arms company for the Volcanic rifle. During WWII, Germany began an intensive program to research and develop a practical caseless ammunition for military use, which was driven by the rising scarcity of metals, especially copper used to make cartridge cases. The Germans had some success, but not sufficient enough to produce a caseless cartridge system during the war. Modern caseless ammunition Modern caseless ammunition consists of a solid mass of propelland, originally nitrocellulose, cast into shape to form the body of the cartridge, with cavities to accept the bullet and a primer, preferably combustable, which are glued into place. The completed cartridge might also contain a booster charge of powdered propellant, to help ignite the body and provide initial thrust to the bullet. Many caseless cartridges are also telescoped, with the bulk of the bullet held within the body of the cartridge, to cut down on cartridge length. A shorter cartridge cuts down on the distance the firearm's action must reciprocate to load a new round, which allows for higher cyclic rates and greater probability of multiple hits on a target at long range. Lack of a case also reduces the bullet's weight substantially, especially in small-bore rifles. For example, the caseless ammuniton for the Voere VEC-91 weighs about one third as much as regular ammunition for the same caliber. While it seems a simple operation to replace the case with a piece of solid propellant, the cartridge case provides more than just a way to keep the cartridge componets together, and these other funtions must be replaced if the cartridge is to be replaced. Caseless ammuition is not without its drawbacks, and it is these drawbacks that have kept modern caseless ammunition from achieving wider success. Heat sensitivity The first major problem, of great concern to the military, is the heat sensitivity of the ammunition. Nitrocellulose, the primary component of modern gunpowder, ignites at a very low temperature of around 170 degrees Celsius. One of the functions of the metallic cartridge case is as a heat sink; the metallic case carries away a significant amount of heat from combustion of the propellant, slowing the rate at which heat is transferred to the chamber. The thermal insulation also works the other way around, shielding the charge from built up heat from the chamber walls. Without a case to provide these functions, caseless rounds using nitrocellulose will begin to cook off, firing from residual chamber heat, much sooner than normal cartridges would. The normal solution to the problem of heat is to increase the heat resistance by switching to a propellant with a higher ignition temperature, typically a non-crystalline explosive carefully formulated to provide an appropriate rate of combustion. Sealing Another important function provided by the cartridge is to seal the rear of the chamber. During firing of a cased cartridge, the pressure in the chamber expands the brass and blocks the chamber. This prevents gas exiting from the rear of the chamber, and it has also been experimentally shown to provide a significant amount of support to the bolt. Without the case to provide this seal, the firearm design must account for this and provide a means of sealing the rear of the chamber. This problem was also encountered with the Dreyse needle gun; the French Chassepot solved the leaking breech problem with the addition of a rubber seal to the bolt. Telescoping caseless rounds must also deal with the issue of blocking the bore, as the bullet is surrounded by propellant. The booster charge is used to address this issue, providing an initial burst of pressure to force the bullet out of the cartridge body and into the barrel before the body combusts. Fragility Caseless rounds are limited by the fact that the cartridge body is primarily a propellant, and structural properties are secondary to the combustion properties. The primary issue is one of extraction. While caseless ammunition elimitates the need to extract a fired case, unfired cases must be extracted in case of a misfire, or to unload the firearm. In metallic cases, this ability is provided by a rim or extractor groove machined into the rear of the case. Even in completely plastic bodies cartridges, such as the Activ brand shotgun shells, a thin metal ring is molded into the rim to provide support for the extractor. Modern Caseless firearms One of the first caseless firearm and ammunition systems produced was actually made by Daisy, the airgun maker, in 1968. The V/L Rifle used a .22 caliber (5.5mm) low powered caseless round with no primer. The rifle was basically a spring-piston air rifle, but when used with the V/L ammunition the energy from the compression of the piston heated the air behind the cartridge enough to ignite the propellant, and this generated the bulk of the energy of firing. The Daisy V/L Rifle system was discontinued in 1969 after the ATF ruled that it was not an airgun, but a firearm, which Daisy did not have the license to produce. Several assault rifles have used caseless ammunition. One of the better-known weapons of this type is the G11 made by Heckler & Koch. Although the rifle never entered full production, it went through a number of prototype stages as well as field testing before being put aside in favor of a more conventional firearm, the G36c, which is also cheaper. The first commerical caseless rifle featuring electronic firing was the Voere VEC-91. In January 1969, the US Army deployed their then new aluminum built M551 Sheridan tanks to Vietnam. The Sheridan fired combustable-cased amunition from its 152mm main gun. When the breech was opened after firing, only smoke exited from the chamber. The Rheinmetall RMK30 was designed to use 30x250mm caseless rounds. Crye Associates submitted a rifle design, The Modular Rifle-Caseless as a competing firearm for the upcoming OICW competition, but the design never made it past the prototype stage. Category:Weapons